Thermal detector, thermal detection device, and electronic instrument

ABSTRACT

A thermal detector includes a thermal detection element, a support member, and a fixing part supporting the support member. The support member mounts and supports the thermal detection element on a second side thereof with a first side thereof facing a cavity. The support member includes a first layer member disposed on the second side and having a residual stress in a first direction, and a second layer member laminated on the first layer member on the first side and having a residual stress in a second direction opposite to the first direction. A thermal conductance of the first layer member is less than a thermal conductance of the second layer member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2010-072081 filed on Mar. 26, 2010. The entire disclosure of JapanesePatent Application No. 2010-072081 is hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to a thermal detector, a thermal detectiondevice, and an electronic instrument or the like.

2. Related Art

Known thermal detection devices include pyroelectric or bolometer-typeinfrared detection devices. An infrared detection device utilizes achange (pyroelectric effect or pyroelectronic effect) in the amount ofspontaneous polarization of a pyroelectric material according to thelight intensity (temperature) of received infrared rays to create anelectromotive force (charge due to polarization) at both ends of thepyroelectric body (pyroelectric-type) or vary a resistance valueaccording to the temperature (bolometer-type) and detect the infraredrays. Compared with a bolometer-type infrared detection device, apyroelectric infrared detection device is complex to manufacture, buthas the advantage of excellent detection sensitivity.

A cooling device is usually not included in the structure of a thermaldetection element. It is therefore necessary to adopt a structure inwhich the element is housed in an airtight package, the element isplaced in a reduced-pressure environment and thermally separated fromthe substrate or the peripheral layers, and heat evolved by receivedlight (infrared rays or other light) is kept as much as possible fromdiffusing into the surrounding area. An example of an effective means ofpreventing prevent heat from dissipating into the substrate, and ofsuppressing reductions in the detection characteristics of the thermaldetection element, is to employ a structure in which a cavity forthermal separation is provided between the substrate and the thermaldetection element (see Japanese Laid-Open Patent Publication No.2000-205944 and Japanese Laid-Open Patent Publication No. 2002-214038,for example). Japanese Laid-Open Patent Publication No. 2000-205944discloses a thermal infrared array sensor which has a cavity for thermalseparation, and Japanese Laid-Open Patent Publication No. 2002-214038discloses a pyroelectric infrared detection element which has a cavityfor thermal separation.

SUMMARY

The thermal detection element is mounted on a membrane supported on asubstrate. A cavity is formed between the membrane and the substrate ina region opposite the thermal detection element. In the manufacturingprocess, a sacrificial layer is formed so as to be embedded in thecavity of the substrate, the membrane is formed on the sacrificiallayer, and the thermal detection element is then formed on the membrane.

In this manufacturing process, the membrane is flat insofar as thesacrificial layer is flat, but it has been discovered that a curvatureoccurs in the membrane when the sacrificial layer is removed byisotropic etching in the final step.

An object of the several aspects of the present invention is to providea thermal detector whereby curvature in the member for supporting thethermal detection element can be suppressed, and to provide a thermaldetection device and an electronic instrument.

A thermal detector according to an aspect of the present inventionincludes a thermal detection element, a support member and a fixingpart. The support member has a first side and a second side oppositefrom the first side. The support member mounts and supports the thermaldetection element on the second side with the first side facing acavity. The support member includes a first layer member having aresidual stress in a first direction, the first layer member beingdisposed on the second side of the support member, and a second layermember having a residual stress in a second direction opposite to thefirst direction. The second layer member is laminated on the first layermember on the first side of the support member. A thermal conductance ofthe first layer member is less than a thermal conductance of the secondlayer member. The fixing part supports the support member.

According to this aspect, since a residual compression stress occurs inthe first layer member, and a residual tensile stress occurs in thesecond layer member of the support member, for example, stresses inmutually opposite directions act so as to cancel out, and residualstress in the support member as a whole is reduced or eliminated.Curvature of the support member can thereby be suppressed. In thesupport member formed by different types of members, the thermalconductance of the first layer member adjacent to the thermal detectionelement is less than the thermal conductance of the second layer member,and dissipation of heat from the thermal detection element can therebyalso be reduced.

In the thermal detector as described above, the support memberpreferably further includes a third layer member laminated on the secondlayer member so that the second layer member is disposed between thefirst layer member and the third layer member, and the third layermember has a residual stress in the first direction.

Through this configuration, the residual stress that could not be fullysuppressed by only a two-layer member can be further suppressed by thethird layer member, and residual stress in the support member as a wholecan be further reduced or eliminated.

In the thermal detector as described above, one of the first layermember and the second layer member preferably includes an oxide layer,and the other of the first layer member and the second layer memberincludes a nitride layer. Through this configuration, since an oxidelayer and a nitride layer has stress in opposite directions, it ispossible to reduce stress that causes curvature in the support member.

In the thermal detector as described above, the first layer member andthe third layer member are preferably made of the same material. Thestrong residual stress of a nitride layer is cancelled out by theoppositely directed residual stress of two layers of oxide layers, andit is possible to reduce stress that causes curvature in the supportmember.

In the thermal detector as described above, the thermal detectionelement preferably includes a capacitor in which an amount ofpolarization varies based on a temperature, the capacitor having apyroelectric body between a first electrode and a second electrode. Inother words, the thermal detector according to this configuration isdefined as being applied to a pyroelectric optical detector.

In the thermal detector as described above, one of the first layermember and the second layer member preferably has reducing gas barrierproperties.

In a pyroelectric optical detector, the characteristics of thepyroelectric body of the capacitor are degraded when oxygen deficitoccurs due to reducing gas. Reductive obstructive factors from the sideof the support member can be blocked by a reducing gas barrier layerdisposed within the support member, by providing reducing gas barrierproperties to one of the first layer member and second layer memberwhich constitute the support member.

The thermal detector as described above preferably further includes areducing gas barrier layer coating at least a side surface of thecapacitor. The second layer member preferably has reducing gas barrierproperties.

Evaporation vapor is sometimes formed inside the capacitor in the bakingstep of the pyroelectric body and during other high-temperatureprocessing, but an escape route for this vapor is maintained by thefirst layer member of the support member.

In the thermal detector as described above, the first electrodepreferably includes an orientation control layer that controlsorientation of the pyroelectric body, and an adhesive layer thatincreases adhesion to the first layer member of the support member, theadhesive layer being disposed further toward the support member than theorientation control layer.

Since the orientation control properties of the orientation controllayer degrade when there are surface irregularities or voids against thebase layer, the adhesive layer is provided to maintain the orientationcontrol properties.

In the thermal detector as described above, the support memberpreferably includes an etching stop layer on an outermost layer on thesecond side, the etching stop layer being formed on a sacrificial layerdisposed in the cavity and left as the outermost layer on the secondside of the support member after removal of the sacrificial layer.

An etching stop layer may be necessary when the material of the supportmember is highly nonselective to etching with respect to the material ofthe sacrificial layer. This etching stop layer may also contribute toalleviating the stress of the support member. In other words, theetching stop layer may also serve as a second layer member or thirdlayer member, or may be added as a fourth layer member.

In the thermal detector as described above, the etching stop layerpreferably has reducing gas barrier properties. In other words, theetching stop layer may demonstrate reducing gas barrier properties evenin a case in which the etching stop layer also serves to alleviate thestress of the second layer member or third layer member of the supportmember, or in a case in which the etching stop layer is added as afourth layer member. The etching stop layer may thereby reinforce orsupplement as a barrier layer for reductive obstructive factors from theside of the support member of the capacitor.

A thermal detection device according to another aspect of the presentinvention includes a plurality of the thermal detectors described abovearranged in two dimensions along two axes. In this thermal detectiondevice, the detection sensitivity is increased in the thermal detectorof each cell, and a distinct light (temperature) distribution image cantherefore be provided.

An electronic instrument according to another aspect of the presentinvention has the thermal detector or thermal detection device describedabove. By using one or a plurality of cells of the thermal detector as asensor, the electronic instrument is most suitable in thermography foroutputting a light (temperature) distribution image, in automobilenavigation and surveillance cameras as well as object analysisinstruments (measurement instruments) for analyzing (measuring) physicalinformation of objects, in security instruments for detecting fire orheat, in FA (Factory Automation) instruments provided in factories orthe like, and in other applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIGS. 1A through 1D are simplified views showing the mechanism by whichcurvature occurs (FIGS. 1A through 1C) in the support member formounting the thermal detection element according to comparativeexamples, and the mechanism by which occurrence of curvature issuppressed (FIG. 1D) in the support member for mounting the thermaldetection element according to an embodiment of the present invention;

FIG. 2 is a simplified plan view showing the pyroelectric infrareddetection device according to an embodiment of the present invention;

FIG. 3 is a simplified sectional view showing the pyroelectric detectorof one cell of the pyroelectric infrared detection device shown in FIG.2;

FIG. 4 is a simplified sectional view showing a manufacturing step, andshows the support member and infrared detection element formed on thesacrificial layer;

FIG. 5 is a simplified sectional view showing a modification in whichthe reducing gas barrier properties in the vicinity of the wiring plugare enhanced;

FIG. 6 is a simplified sectional view showing the capacitor structure ofthe pyroelectric infrared detector according to an embodiment of thepresent invention;

FIG. 7 is a block diagram showing the electronic instrument whichincludes the thermal detector or thermal detection device; and

FIGS. 8A and 8B are views showing an example of the configuration of apyroelectric optical detection device in which pyroelectric opticaldetectors are arranged in two dimensions.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the present invention will be described indetail. The embodiments described below do not unduly limit the scope ofthe present invention as recited in the claims, and all of theconfigurations described in the embodiments are not necessarilyessential means of achievement of the present invention.

1. Thermal Infrared Detection Device

FIG. 2 shows a pyroelectric infrared detection device (one example of athermal detection device) in which a plurality of cells of pyroelectricinfrared detectors (one example of thermal detectors) is arranged alongtwo orthogonal axes, the pyroelectric infrared detector of each cellbeing provided with a support member in which curvature occurring in themanner shown in FIGS. 1A through 1C described hereinafter is overcome asshown in FIG. 1D, and a pyroelectric optical detection element (oneexample of a thermal detection element) mounted on the support member. Apyroelectric infrared detection device may also be formed by apyroelectric infrared detector of a single cell. In FIG. 2, a pluralityof posts 104 is provided upright from a base part (also referred to as afixing part) 100, and pyroelectric infrared detectors 200, each cell ofwhich is supported by two posts 104, for example, are arranged along twoorthogonal axes. The area occupied by each cell of pyroelectric infrareddetectors 200 is 30×30 μm, for example.

As shown in FIG. 2, each pyroelectric infrared detector 200 includes asupport member (membrane) 210 linked to two posts 104, and an infrareddetection element (one example of a thermal detection element) 220. Thearea occupied by the pyroelectric infrared detection element 220 of onecell is 10×10 μm, for example.

Besides being connected to the two posts 104, the pyroelectric infrareddetector 200 of each cell is in a non-contacting state, a cavity 102(see FIG. 3) is formed below the pyroelectric infrared detector 200, andopen parts 102A communicated with the cavity 102 are provided on theperiphery of the pyroelectric infrared detector 200 in plan view. Thepyroelectric infrared detector 200 of each cell is thereby thermallyseparated from the base part 100 as well as from the pyroelectricinfrared detectors 200 of other cells.

The support member 210 has a mounting part 210A for mounting andsupporting the pyroelectric infrared detection element 220, and two arms210B linked to the post 104. The two arms 210B are formed so as toextend redundantly and with a narrow width in order to thermallyseparate the pyroelectric infrared detection element 220.

FIG. 2 is a plan view which omits the members above the wiring layersconnected to the upper electrodes, and FIG. 2 shows a first electrode(lower electrode) wiring layer 222 and a second electrode (upperelectrode) wiring layer 224 connected to the pyroelectric infrareddetection element 220. The first and second electrode wiring layers 222,224 extend along the arms 210B, and are connected to a circuit insidethe base part 100 via the posts 104. The first and second electrodewiring layers 222, 224 are also formed so as to extend redundantly andwith a narrow width in order to thermally separate the pyroelectricinfrared detection element 220.

2. Overview of the Pyroelectric Infrared Detector

FIG. 3 is a sectional view showing the pyroelectric infrared detector200 shown in FIG. 2. FIG. 4 is a partial sectional view showing thepyroelectric infrared detector 200 during the manufacturing process. InFIG. 4, the cavity 102 is embedded by a sacrificial layer 150. Thesacrificial layer 150 is present from before the step of forming thesupport member 210 and the pyroelectric infrared detection element 220until after this formation step, and is removed by isotropic etchingafter the step of forming the pyroelectric infrared detection element220.

As shown in FIG. 3, the base part 100 includes a substrate, e.g., asilicon substrate 110, and a spacer layer 120 formed by an interlayerinsulation layer on the silicon substrate 110. The post 104 is formed byetching the spacer layer 120. A plug 106 connected to one of the firstand second electrode wiring layers 222, 224 may be disposed at the post104. The plug 106 is connected to a row selection circuit (row driver)provided to the silicon substrate 110, or a read circuit for readingdata from an optical detector via a column line. The cavity 102 isformed at the same time as the post 104 by etching the spacer layer 120.The open parts 102A shown in FIG. 2 are formed by pattern etching thesupport member 210.

The pyroelectric infrared detection element 220 mounted on the supportmember 210 includes a capacitor 230. The capacitor 230 includes apyroelectric body 232, a first electrode (lower electrode) 234 connectedto the lower surface of the pyroelectric body 232, and a secondelectrode (upper electrode) 236 connected to the upper surface of thepyroelectric body 232. The first electrode 234 may include an adhesivelayer 234D for increasing adhesion to a first layer member (e.g., SiO₂)of the support member 210.

The capacitor 230 is covered by a reducing gas barrier layer 240 forsuppressing penetration of reducing gas (hydrogen, water vapor, OHgroups, methyl groups, and the like) into the capacitor 230 during stepsafter formation of the capacitor 230. The reason for this is that thepyroelectric body (e.g., PZT or the like) 232 of the capacitor 230 is anoxide, and when an oxide is reduced, oxygen deficit occurs and thepyroelectric effects are compromised.

The reducing gas barrier layer 240 includes a first barrier layer 242and a second barrier layer 244, as shown in FIG. 4. The first barrierlayer 242 can be formed by forming a layer of aluminum oxide Al₂O₃, forexample, by sputtering. Since reducing gas is not used in sputtering, noreduction of the capacitor 230 occurs. The second barrier layer 244 canbe formed by forming a layer of aluminum oxide Al₂O₃, for example, byAtomic Layer Chemical Vapor Deposition (ALCVD), for example. Common CVD(Chemical Vapor Deposition) methods use reducing gas, but the capacitor230 is isolated from the reducing gas by the first barrier layer 242.

The total layer thickness of the reducing gas barrier layer 240 hereinis 50 to 70 nm, e.g., 60 nm. At this time, the layer thickness of thefirst barrier layer 242 formed by CVD is greater than that of the secondbarrier layer 244 formed by Atomic Layer Chemical Vapor Deposition(ALCVD), and is 35 to 65 nm, e.g., 40 nm, at minimum. In contrast, thelayer thickness of the second barrier layer 244 formed by Atomic LayerChemical Vapor Deposition (ALCVD) can be reduced; for example, a layerof aluminum oxide Al₂O₃ is formed having a thickness of 5 to 30 nm,e.g., 20 nm. Atomic Layer Chemical Vapor Deposition (ALCVD) hasexcellent embedding characteristics in comparison with sputtering andother methods, and can therefore be adapted for miniaturization, and thereducing gas barrier properties in the first and second barrier layers242, 244 can be enhanced. The first barrier layer 242 formed bysputtering is not fine in comparison with the second barrier layer 244,but this aspect contributes to lowering the heat transfer rate thereof,and dissipation of heat from the capacitor 230 can therefore beprevented.

An interlayer insulation layer 250 is formed on the reducing gas barrierlayer 240. Hydrogen gas, water vapor, or other reducing gas usually isformed when the starting material gas (TEOS) of the interlayerinsulation layer 250 chemically reacts. The reducing gas barrier layer240 provided on the periphery of the capacitor 230 protects thecapacitor 230 from the reducing gas that occurs during formation of theinterlayer insulation layer 250.

The first electrode (lower electrode) wiring layer 222 and secondelectrode (upper electrode) wiring layer 224 shown in FIG. 2 as well aredisposed on the interlayer insulation layer 250. A first contact hole252 and second contact hole 254 are formed in advance in the interlayerinsulation layer 250 before formation of the electrode wiring. At thistime, a contact hole is formed in the same manner in the reducing gasbarrier layer 240 as well. The first electrode (lower electrode) 234 andthe first electrode wiring layer 222 are made continuous by a first plug226 embedded in the first contact hole 252. The second electrode (upperelectrode) 236 and the second electrode wiring layer 224 are madecontinuous in the same manner by a second plug 228 embedded in thesecond contact hole 254.

When the interlayer insulation layer 250 is not present in thisarrangement, during pattern etching of the first electrode (lowerelectrode) wiring layer 222 and the second electrode (upper electrode)wiring layer 224, the second barrier layer 244 of the reducing gasbarrier layer 240 beneath is etched, and the barrier properties thereofare reduced. The interlayer insulation layer 250 may be necessary inorder to secure the harrier properties of the reducing gas barrier layer240.

The interlayer insulation layer 250 preferably has a low hydrogencontent. The interlayer insulation layer 250 is therefore degassed byannealing. The hydrogen content of the interlayer insulation layer 250is thereby made lower than that of a passivation layer 260 for coveringthe first and second electrode wiring layers 222, 224.

Since the reducing gas barrier layer 240 at the top of the capacitor 230is devoid of contact holes and closed when the interlayer insulationlayer 250 is formed, the reducing gas during formation of the interlayerinsulation layer 250 does not penetrate into the capacitor 230. However,the barrier properties decline after the contact hole is formed in thereducing gas barrier layer 240. As an example of a technique forpreventing this phenomenon, the first and second plugs 226, 228 areformed by a plurality of layers 228A, 228B (only the second plug 228 isshown in FIG. 4), as shown in FIG. 4, and a barrier metal layer is usedin the first layer 228A. Reducing gas barrier properties are ensured bythe barrier metal of the first layer 228A. Highly diffusible metals suchas titanium Ti are not preferred as the barrier metal of the first layer228A, and titanium aluminum nitride TiAlN, which has minimaldiffusibility and high reducing gas barrier properties, can be used. Areducing gas barrier layer 290 may be additionally provided so as tosurround at least the second plug 228 as shown in FIG. 5, as a methodfor stopping the penetration of reducing gas from the contact hole. Thisreducing gas barrier layer 290 may also serve as the barrier metal 228Aof the second plug 228, or the barrier metal 228A may be removed. Thereducing gas barrier layer 290 may also coat the first plug 226.

The SiO₂ or SiN passivation layer 260 is provided so as to cover thefirst and second electrode wiring layers 222, 224. An infrared-absorbingbody (one example of a light-absorbing member) 270 is provided on thepassivation layer 260 above at least the capacitor 230. The passivationlayer 260 is also formed from SiO₂ or SiN, but is preferably formed froma different type of material which has a high etching selection ratiowith respect to the passivation layer 260 below, due to the need forpattern etching of the infrared-absorbing body 270. Infrared rays areincident on the infrared-absorbing body 270 from the direction of thearrow in FIG. 2, and the infrared-absorbing body 270 evolves heat inaccordance with the amount of infrared rays absorbed. This heat istransmitted to the pyroelectric body 232, whereby the amount ofspontaneous polarization of the capacitor 230 varies according to theheat, and the infrared rays can be detected by detecting the charge dueto the spontaneous polarization. The infrared-absorbing body 270 is notlimited to being provided separately from the capacitor 230, and neednot be provided separately in a case in which the infrared-absorbingbody 270 is present within the capacitor 230.

Even when reducing gas is generated during CVD formation of thepassivation layer 260 or the infrared-absorbing body 270, the capacitor230 is protected by the reducing gas barrier layer 240 and the barriermetals in the first and second plugs 226, 228.

A reducing gas barrier layer 280 is provided so as to cover the externalsurface of the pyroelectric infrared detector 200 which includes theinfrared-absorbing body 270. The reducing gas barrier layer 280 must beformed with a smaller thickness than the reducing gas barrier layer 240,for example, in order to increase the transmittance of infrared rays (inthe wavelength spectrum of 8 to 14 μm) incident on theinfrared-absorbing body 270. For this purpose, Atomic Layer ChemicalVapor Deposition (ALCVD) is used, which is capable of adjusting thelayer thickness at a level corresponding to the size of an atom. Thereason for this is that the layer formed by a common CVD method is toothick, and infrared transmittance is adversely affected. In the presentembodiment, a layer is formed having a thickness of 10 to 50 nm, e.g.,20 nm, from aluminum oxide Al₂O₃, for example. As described above,Atomic Layer Chemical Vapor Deposition (ALCVD) has excellent embeddingcharacteristics in comparison with sputtering and other methods, and istherefore adapted to miniaturization, a precise layer can be formed atthe atomic level, and reducing gas barrier properties can be increasedeven in a thin layer.

On the side of the base part 100, an etching stop layer 130 for useduring isotropic etching of the sacrificial layer 150 (see FIG. 4)embedded in the cavity 102 in the process of manufacturing thepyroelectric infrared detector 200 is formed on a wall part for definingthe cavity 102, i.e., a side wall 104A and a bottom wall 100A fordefining the cavity. An etching stop layer 140 is formed in the samemanner on a lower surface (upper surface of the sacrificial layer 150)of the support member 210. In the present embodiment, the reducing gasbarrier layer 280 is formed from the same material as the etching stoplayers 130, 140. In other words, the etching stop layers 130, 140 alsohave reducing gas barrier properties. The etching stop layers 130, 140are also formed by forming layers of aluminum oxide Al₂O₃ at a thicknessof 20 to 50 nm by Atomic Layer Chemical Vapor Deposition (ALCVD).

Since the etching stop layer 140 has reducing gas barrier properties,when the sacrificial layer 150 is isotropically etched by hydrofluoricacid in a reductive atmosphere, it is possible to keep the reducing gasfrom passing through the support member 210 and penetrating into thecapacitor 230. Since the etching stop layer 130 for covering the basepart 100 has reducing gas barrier properties, it is possible to keep thetransistors or wiring of the circuit in the base part 100 from beingreduced and degraded.

3. Structure of the Support Member

FIGS. 1A through 1D are simplified views showing the mechanism by whichcurvature occurs and is eliminated in the support member for mountingthe thermal detection element according to an embodiment of the presentinvention. As shown in FIG. 1A, in a state in which the sacrificiallayer 150 is embedded in the cavity 102 of the base part 100, thesupport member 210 is formed so that both ends thereof are joined to thebase part 100, and the pyroelectric infrared detection element 220 issubsequently formed. In this state, after the sacrificial layer 150 isformed so as to be embedded in the cavity 102, the top surface of thesacrificial layer 150 is flattened by CMP or another method. The supportmember 210 is thereby also flat insofar as the top surface of thesacrificial layer 150 is flat.

The sacrificial layer 150 is then removed by isotropic etching. Themoment the sacrificial layer 150 is removed, the support member 210flexes and curves to the extent that residual stress is present in thesupport member 210.

In FIG. 1B, when a residual compression stress CS is present in thesupport member 210, a bending moment M1 acts at both ends of the supportmember 210. A curvature then occurs in the support member 210 such thatthe support member 210 is downwardly convex.

In FIG. 1C, when a residual tensile stress TS is present in the supportmember 210, a bending moment M2 acts at both ends of the support member210. A curvature then occurs in the support member 210 such that thesupport member 210 is upwardly convex.

As shown in FIGS. 1B and 1C, residual stress occurring in the materialfrom which the support member 210 is formed causes the support member210 to curve so as to be upwardly convex or downwardly convex. Althoughcurvature does not occur in the manufacturing process in which thesacrificial layer 150 is present, as shown in FIG. 1A, the supportmember 210 becomes curved in the final step.

In the present embodiment, the support member 210, in which curvatureoccurs when a single material is used, is formed by laminating first andsecond layer members 212, 214 which are formed by a plurality ofdifferent types of materials. In other words, the characteristics shownin FIG. 1B, for example, occur in the first layer member 212 alone, andthe characteristics shown in FIG. 1C, for example, occur in the secondlayer member 214 alone, but by laminating these members, the curvatureof the support member 210 is suppressed as shown in FIG. 1D. The reasonfor this is that the residual compression stress CS, for example, thatoccurs in the first layer member 212, and the residual tensile stress TSthat occurs in the second layer member 214 are directed so as to canceleach other out. In other words, the residual compression stress CS actsin one direction, and the residual tensile stress TS acts in theopposite direction.

Specifically, one of the first layer member 212 and second layer member214 may be formed by an oxide layer and the other by a nitride layer.Through this configuration, since the oxide layer and the nitride layerhave stress in opposite directions, stress which causes curvature of thesupport member 210 can be reduced. In the support member 210 formed bydifferent types of materials, the thermal conductance of the first layermember 212 adjacent to the pyroelectric infrared detection element 220is less than the thermal conductance of the second layer member 214, anddissipation of heat from the pyroelectric infrared detection element 220can thereby also be reduced. For example, the first layer member 212 maybe made of material having a lower thermal conductivity than material ofthe second layer member 214, and/or a thickness of the first layermember 212 may be made larger than a thickness of the second layer 214since a thermal conductance of a layer is proportional to a thermalconductivity of the layer and inversely proportional a thickness of thelayer.

In the support member 210 on which the capacitor 230 is mounted in theembodiment shown in FIG. 4, since residual stress causes curvature tooccur when a single layer is used, the support member 210 may be formedby three layers, for example, so that the stress that causes curvatureis cancelled out by the residual stresses of both tension andcompression, as shown in FIGS. 6 and 4.

In order from the capacitor 230 side, the first layer member 212 iscomposed of an oxide layer (e.g., SiO₂), the second layer member 214 iscomposed of a nitride layer (e.g., Si₃N₄), and a third layer member 216is composed of an oxide layer (e.g., SiO₂, the same as the first layermember 212). Through this configuration, the residual stress that couldnot be fully suppressed by only the two layers of the first and secondlayer members 212, 214 shown in FIG. 1D can be further suppressed by thethird layer member 216, and residual stress in the support member as awhole can be further reduced or eliminated. In particular, the strongresidual stress of the nitride layer of the second layer member 214 iscancelled out by the oppositely directed residual stress of two layersof oxide layers above and below which constitute the first and thirdlayer members 212, 216, and it is possible to reduce stress that causescurvature in the support member 210.

Since a nitride layer (e.g., Si₃N₄) has reducing gas barrier properties,the support member 210 also functions to block reductive obstructivefactors from penetrating from the side of the support member 210 to thepyroelectric body 232 of the capacitor 230.

4. Structure of the Capacitor 4.1 Thermal Conductance

FIG. 6 is a simplified sectional view showing the relevant parts of thepresent embodiment. As described above, the capacitor 230 includes apyroelectric body 232 between the first electrode (lower electrode) 234and the second electrode (upper electrode) 236. The capacitor 230 ismounted and supported on a second surface or second side (upper surfaceor upper side in FIG. 6) opposite a first surface or first side (lowersurface or lower side in FIG. 6) at which the support member 210 facesthe cavity 102. Infrared rays can be detected by utilizing a change(pyroelectric effect or pyroelectronic effect) in the amount ofspontaneous polarization of the pyroelectric body 232 according to thelight intensity (temperature) of the incident infrared rays. In thepresent embodiment, the incident infrared rays are absorbed by theinfrared-absorbing body 270, heat is evolved by the infrared-absorbingbody 270, and the heat evolved by the infrared-absorbing body 270 istransmitted via a solid heat transfer path between theinfrared-absorbing body 270 and the pyroelectric body 232.

In the capacitor 230 of the present embodiment, the thermal conductanceG1 of the first electrode (lower electrode) 234 adjacent to the supportmember 210 is less than the thermal conductance G2 of the secondelectrode (upper electrode) 236. Through this configuration, the heatcaused by the infrared rays is readily transmitted to the pyroelectricbody 232 via the second electrode (upper electrode) 236, the heat of thepyroelectric body 232 does not readily escape to the support member 210via the first electrode (lower electrode) 234, and the signalsensitivity of the infrared detection element 220 is enhanced.

The structure of the capacitor 230 having the characteristics describedabove will be described in further detail with reference to FIG. 6.First, the thickness T1 of the first electrode (lower electrode) 234 isgreater than that of the second electrode (upper electrode) 236 (T1>T2).The thermal conductance G1 of the first electrode (lower electrode) 234is such that G1=λ1/T1, where λ1 is the thermal conductivity of the firstelectrode (lower electrode) 234. The thermal conductance G2 of thesecond electrode (upper electrode) 236 is such that G2=λ2/T2, where λ2is the thermal conductance of the second electrode (upper electrode)236.

In order to obtain a thermal conductance relationship of G1<G2, when thefirst and second electrodes 234, 236 are both formed from the samesingle material, such as platinum Pt or iridium Ir, then λ1=λ2, andT1>T2 from FIG. 6. The relationship G1<G2 can therefore be satisfied.

A case in which the first and second electrodes 234, 236 are each formedfrom the same material will first be considered. In the capacitor 230,in order for the crystal direction of the pyroelectric body 232 to bealigned, it is necessary to align the crystal lattice level of theboundary of the lower layer on which the pyroelectric body 232 is formedwith the first electrode 234. In other words, although the firstelectrode 234 has the function of a crystal seed layer, platinum Pt hasstrong self-orienting properties and is therefore preferred as the firstelectrode 234. Iridium Ir is also suitable as a seed layer material.

In the second electrode (upper electrode) 236, the crystal orientationsare preferably continuously related from the first electrode 234 throughthe pyroelectric body 232 and the second electrode 236, without breakingdown the crystal properties of the pyroelectric body 232. The secondelectrode 236 is therefore preferably formed from the same material asthe first electrode 234.

When the second electrode 236 is thus formed by the same material, e.g.,Pt, Ir, or another metal, as the first electrode 234, the upper surfaceof the second electrode 236 can be used as a reflective surface. In thiscase, as shown in FIG. 6, the distance L from the top surface of theinfrared-absorbing body 270 to the top surface of the second electrode236 is preferably λ/4 (where λ is the detection wavelength of infraredrays). Through this configuration, multiple reflection of infrared raysof the detection wavelength λ occurs between the top surface of theinfrared-absorbing body 270 and the top surface of the second electrode236, and infrared rays of the detection wavelength λ can therefore beefficiently absorbed by the infrared-absorbing body 270.

4.2 Electrode Multilayer Structure

The structure of the capacitor 230 of the present embodiment shown inFIG. 6 will next be described. In the capacitor 230 shown in FIG. 6, thepriority orientation directions of the pyroelectric body 232, the firstelectrode 234, and the crystal orientation of the second electrode 236are aligned with the (111) plane direction, for example. Through apriority orientation in the (111) plane direction, the orientation rateof (111) orientation with respect to other plane directions iscontrolled to 90% or higher, for example. The (100) orientation or otherorientation is more preferred than the (111) orientation in order toincrease the pyroelectric coefficient, but the (111) orientation is usedso as to make polarization easy to control with respect to the appliedfield direction. However, the priority orientation direction is notlimited to this configuration.

The first electrode 234 may include, in order from the support member210, an orientation control layer (e.g., Ir) 234A for controlling theorientation so as to give the first electrode 234 a priority orientationin the (111) plane, for example, a first reducing gas barrier layer(e.g., IrOx) 234B, and a priority-oriented seed layer (e.g., Pt) 234C.

The second electrode 236 may include, in order from the pyroelectricbody 232, an orientation alignment layer (e.g., Pt) 236A in which thecrystal alignment is aligned with the pyroelectric body 232, a secondreducing gas barrier layer (e.g., IrOx) 236B, and a low-resistance layer(e.g., Ir) 236C for lowering the resistance of the bonded surface withthe second plug 228 connected to the second electrode 236.

The first and second electrodes 234, 236 of the capacitor 230 areprovided with a multilayer structure in the present embodiment so thatthe pyroelectric infrared detection element 220 is processed withminimal damage and without reducing the capability thereof despite thesmall heat capacity thereof, the crystal lattice levels are aligned ateach boundary, and the pyroelectric body (oxide) 232 is isolated fromreducing gas even when the periphery of the capacitor 230 is exposed toa reductive atmosphere during manufacturing or use.

The pyroelectric body 232 is formed by growing a crystal of PZT (leadzirconate titanate: generic name for Pb(Zr, Ti)O₃), PZTN (generic namefor the substance obtained by adding Nb to PZT), or the like with apriority orientation in the (111) plane direction, for example. The useof PZTN is preferred, because even a thin layer is not readily reduced,and oxygen deficit can be suppressed. In order to obtain directionalcrystallization of the pyroelectric body 232, directionalcrystallization is performed from the stage of forming the firstelectrode 234 as the layer under the pyroelectric body 232.

The Ir layer 234A for functioning as an orientation control layer istherefore formed on the first electrode (lower electrode) 234 bysputtering. A titanium aluminum nitride (TiAlN) layer or a titaniumnitride (TiN) layer, for example, as the adhesive layer 234D may also beformed under the orientation control layer 234A, as shown in FIG. 6. Thereason for this is that adhesion may be difficult to maintain, dependingon the material of the support member 210. When the first layer member212 of the support member 210 positioned beneath the adhesive layer 234Dis formed from SiO₂, the first layer member 212 is preferably formed byan amorphous material or a material having smaller grains thanpolysilicon. The smoothness of the surface of the support member 210 onwhich the capacitor 230 is mounted can thereby be maintained. When thesurface on which the orientation control layer 234A is formed is rough,the irregularities of the rough surface are reflected in the growth ofthe crystal, and a rough surface is therefore not preferred.

In order to isolate the pyroelectric body 232 from reductive obstructivefactors from below the capacitor 230, the IrOx layer 234B forfunctioning as a reducing gas barrier layer in the first electrode 234is used together with the second layer member (e.g., Si₃N₄) of thesupport member 210, and the etching stop layer (e.g., Al₂O₃) 140 of thesupport member 210, which exhibit reducing gas barrier properties. Thereducing gas used in degassing from the base part 100 during baking orother annealing steps of the pyroelectric body (ceramic) 232, or in theisotropic etching step of the sacrificial layer 150, for example, is areductive inhibiting factor.

Evaporation vapor sometimes formed inside the capacitor 230 in thebaking step of the pyroelectric body 232 and during otherhigh-temperature processing, but an escape route for this vapor ismaintained by the first layer member 212 of the support member 210. Inother words, in order to allow evaporation vapor formed inside thecapacitor 230 to escape, it is better to provide gas barrier propertiesto the second layer member 214 than to provide gas barrier properties tothe first layer member 212.

The IrOx layer 234B as such has minimal crystallinity, but the IrOxlayer 234B is in a metal-metal oxide relationship with the Ir layer 234Aand thus has good compatibility therewith, and can therefore have thesame priority orientation direction as the Ir layer 234A.

The Pt layer 234C for functioning as a seed layer in the first electrode234 is a seed layer for the priority orientation of the pyroelectricbody 232, and has the (111) orientation. In the present embodiment, thePt layer 234C has a two-layer structure. The first Pt layer forms thebasis of the (111) orientation, microroughness is formed on the surfaceby the second Pt layer, and the Pt layer 234C thereby functions as aseed layer for priority orientation of the pyroelectric body 232. Thepyroelectric body 232 is in the (111) orientation after the fashion ofthe seed layer 234C.

In the second electrode 236, since the boundaries of sputtered layersare physically rough, trap sites occur, and there is a risk of degradedcharacteristics, the lattice alignment is reconstructed on the crystallevel so that the crystal orientations of the first electrode 234, thepyroelectric body 232, and the second electrode 236 are continuouslyrelated.

The Pt layer 236A in the second electrode 236 is formed by sputtering,but the crystal direction of the boundary immediately after sputteringis not continuous. Therefore, an annealing process is subsequentlyperformed to re-crystallize the Pt layer 236A. In other words, the Ptlayer 236A functions as an orientation alignment layer in which thecrystal orientation is aligned with the pyroelectric body 232.

The IrOx layer 236B in the second electrode 236 functions as a barrierfor reductive degrading factors from above the capacitor 230. Since theIrOx layer 236B has a high resistance value, the Ir layer 236C in thesecond electrode 236 is used to lower the resistance value with respectto the second plug 228. The Ir layer 236C is in a metal oxide-metalrelationship with the IrOx layer 236B and thus has good compatibilitytherewith, and can therefore have the same priority orientationdirection as the IrOx layer 236B.

In the present embodiment, the first and second electrodes 234, 236 thushave multiple layers arranged in the sequence Pt, IrOx, Ir from thepyroelectric body 232, and the materials forming the first and secondelectrodes 234, 236 are arranged symmetrically about the pyroelectricbody 232.

However, the thicknesses of each layer of the multilayer structuresforming the first and second electrodes 234, 236 are asymmetrical aboutthe pyroelectric body 232. The total thickness T1 of the first electrode234 and the total thickness T2 of the second electrode 236 satisfy therelationship (T1>T2) as also described above. The thermal conductivitiesof the Ir layer 234A, IrOx layer 234B, and Pt layer 234C of the firstelectrode 234 are designated as 21, 22, and 23, respectively, and thethicknesses thereof are designated as T11, T12, and T13, respectively.The thermal conductivities of the Ir layer 236C, IrOx layer 236B, and Ptlayer 236A of the second electrode 236 are also designated as λ1, λ2,and λ3, respectively, and the thicknesses thereof are designated as T21,T22, and T23, respectively in the same manner as the first electrode232.

When the thermal conductances of the Ir layer 234A, IrOx layer 234B, andPt layer 234C of the first electrode 234 are designated as G11, G12, andG13, respectively, G11=λ1/T11, G12=λ2/T12, and G13=λ3/T13. When thethermal conductances of the Ir layer 236C, IrOx layer 236B, and Pt layer236A of the second electrode 236 are designated as G21, G22, and G23,respectively, G21=λ1/T21, G2=λ2/T22, and G23=λ3/T23.

Since 1/G1=(1/G11)+(1/G12)+(1/G13), the total thermal conductance G1 ofthe first electrode 234 is expressed by the equation (1) below.

G1=(G11×G12×G13)/(G11×G12+G12×G13+G11×G13)  (1)

In the same manner, since 1/G2=(1/G21)+(1/G22)+(1/G23), the totalthermal conductance G2 of the second electrode 236 is expressed by theequation (2) below.

G2=(G21×G22×G23)/(G21×G22+G22×G23+G21×G23)  (2)

The thicknesses of each layer of the multilayer structures forming thefirst and second electrodes 234, 236 are substantially in therelationships described below under conditions that satisfyT11+T12+T13=T1>T2=T21+T22+T23.

Ir layers 234A, 236C T11:T21=1:0.7

IrOx layers 234B, 236B T12:T22=0.3:1

Pt layers 234C, 236A T13:T23=3:1

The reasons for adopting such layer thickness relationships are asfollows. First, regarding the Ir layers 234A, 236C, since the Ir layer234A in the first electrode 234 functions as an orientation controllayer, a predetermined layer thickness is necessary in order to impartorientation properties, whereas the purpose of the Ir layer 236C of thesecond electrode 236 is to lower resistance, and lower resistance can beobtained the thinner the layer is.

Next, regarding the IrOx layers 234B, 236B, barrier properties againstreductive obstructive factors from below and above the capacitor 230 areobtained by joint use of other barrier layers (the second layer member214, the reducing gas barrier layer 240, and the etching stoplayers/reducing gas barrier layers 140, 280), and the IrOx layer 234B ofthe first electrode 234 is formed having a small thickness, but thethickness of the IrOx layer 236B of the second electrode 236 isincreased to compensate for low barrier properties in the second plug228.

Lastly, regarding the Pt layers 234C, 236A, the Pt layer 234C in thefirst electrode 234 functions as a seed layer for determining thepriority orientation of the pyroelectric body 232, and therefore musthave a predetermined layer thickness, whereas the purpose of the Ptlayer 236A of the second electrode 236 is to function as an orientationalignment layer aligned with the orientation of the pyroelectric body232, and the Pt layer 236A may therefore be formed with a smallerthickness than the Pt layer 234C in the first electrode 234.

The thickness ratio of the Ir layer 234A, IrOx layer 234B, and Pt layer234C of the first electrode 234 is set so that T11:T12:T13=10:3:15, forexample, and the thickness ratio of the Ir layer 236C, IrOx layer 236B,and Pt layer 236A of the second electrode 236 is set so thatT21:T22:T23=7:10:5, for example.

The thermal conductivity λ3 of Pt is equal to 71.6 (W/m·K), and thethermal conductivity λ1 of Ir is equal to 147 (W/m·K), which issubstantially twice the thermal conductivity λ3 of Pt. The thermalconductivity λ2 of IrOx varies according to the temperature or theoxygen/metal ratio (O/M), but does not exceed the thermal conductivityλ1 of Ir. When the layer thickness relationships and thermalconductivity relationships described above are substituted intoEquations (1) and (2) to calculate the size relationship between G1 andG2, it is apparent that G1<G2. Thus, even when the first and secondelectrodes 234, 236 are endowed with a multilayer structure as in thepresent embodiment, the expression G1<G2 is satisfied from therelationship of the thermal conductivities and layer thicknesses.

When the first electrode 234 has the adhesive layer 234D on the bondedsurface with the support member 210 as described above, the thermalconductance C1 of the first electrode 234 is reduced, and therelationship G1<G2 is easily satisfied.

Since the etching mask of the capacitor 230 degrades as etchingproceeds, the side walls of the capacitor 230 acquire a tapered shapewhich is narrower at the top and wider at the bottom as shown in FIG. 6,the more layers are added to the structure. However, since the taperangle with respect to the horizontal surface is about 80 degrees,considering that the total height of the capacitor 230 is on the orderof nanometers, the increase in surface area of the first electrode 234with respect to the second electrode 236 is small. The amount of heattransferred by the first electrode 234 can thereby be kept smaller thanthe amount of heat transferred by the second electrode 236, based on therelationship between the thermal conductance values of the first andsecond electrodes 234, 236.

4.3 Modifications of the Capacitor Structure

A single-layer structure and multilayer structure are described abovefor the first and second electrodes 234, 236 of the capacitor 230, butvarious other combinations of structures are possible which produce thethermal conductance relationship G1<G2 while maintaining the function ofthe capacitor 230.

First, the Ir layer 236C of the second electrode 236 may be omitted. Thereason for this is that in this case, the object of lowering resistanceis achieved in the same manner when Ir, for example, is used as thematerial of the second plug 228. Through this configuration, since thethermal conductance G2 of the second electrode 236 is greater than inthe case shown in FIG. 6, the relationship G1<G2 is easily satisfied. Areflective surface for defining L=λ/4 shown in FIG. 6 takes the place ofthe Pt layer 236A of the second electrode 236 in this case, but amultiple reflection surface can be maintained in the same manner.

Next, the thickness of the IrOx layer 236B in the second electrode 236in FIG. 6 may be made equal to or less than the thickness of the IrOxlayer 234B in the first electrode 234. As described above, since thebarrier properties against reductive obstructive factors from below andabove the capacitor 230 are obtained by joint use of other barrierlayers (the second layer member 214, the reducing gas barrier layer 240,and the etching stop layers/reducing gas barrier layers 140, 280), whenthe reducing gas barrier properties in the second plug 228 are increasedby the configuration shown in FIG. 5, for example, there is no need forthe thickness of the IrOx layer 236B in the second electrode 236 to begreater than the thickness of the IrOx layer 234B in the first electrode234. Through this configuration, the thermal conductance G2 of thesecond electrode 236 further increases, and the relationship G1<G2 iseasier to obtain.

Next, the IrOx layer 234B in the first electrode 234 of FIG. 6 may beomitted. Crystal continuity between the Ir layer 234A and the Pt layer234C is not hindered by omission of the IrOx layer 234B, and no problemsoccur with regard to crystal orientation. When the IrOx layer 234B isomitted, the capacitor 230 has no barrier layer with respect toreductive obstructive factors from below the capacitor 230. However, thesecond layer member 214 is present in the support member 210 forsupporting the capacitor 230, and the etching stop layer 140 is presenton the lower surface of the support member 210, and when the secondlayer member 214 and the etching stop layer 140 are formed by layershaving reducing gas barrier properties, barrier properties with respectto reductive obstructive factors from below the capacitor 230 can bemaintained in the capacitor 230.

When the IrOx layer 234B in the first electrode 234 is omitted in thisarrangement, the thermal conductance G1 of the first electrode 234increases. It may therefore be necessary to increase the thermalconductance G2 of the second electrode 236 as well in order to obtainthe relationship G1<G2. In this case, the IrOx layer 236B in the secondelectrode 236 may be omitted, for example. Once the IrOx layer 236B isomitted, the Ir layer 236C is also no longer necessary. The reason forthis is that the Pt layer 236A functions as a low-resistance layerinstead of the Ir layer 236C. Barrier properties with respect toreductive obstructive factors from above the capacitor 230 can bemaintained by the reducing gas barrier layer 240 described above, thebarrier metal 228A shown in FIG. 4, or the reducing gas barrier layer290 shown in FIG. 5.

When the second electrode 236 shown in FIG. 6 is formed only by the Ptlayer 236A as described above, the first electrode 234 may be formed bythe Pt layer 234C as a single layer, by the Ir layer 234A and Pt layer234C as two layers, or by the Ir layer 234A of FIG. 6, the IrOx layer234B, and the Pt layer 234C as three layers. In any of these cases, therelationship G1<G2 can easily be obtained by making the thickness T11 ofthe Ir layer 234A of the first electrode 234 greater than the thicknessT21 of the Pt layer 236A of the second electrode 236 (T11>T21), forexample.

5. Electronic Instrument

FIG. 7 shows an example of the configuration of an electronic instrumentwhich includes the thermal detector or thermal detection device of thepresent embodiment. The electronic instrument includes an optical system400, a sensor device (thermal detection device) 410, an image processor420, a processor 430, a storage unit 440, an operating unit 450, and adisplay unit 460. The electronic instrument of the present embodiment isnot limited to the configuration shown in FIG. 7, and variousmodifications thereof are possible, such as omitting some constituentelements (e.g., the optical system, operating unit, display unit, orother components) or adding other constituent elements.

The optical system 400 includes one or more lenses, for example, a driveunit for driving the lenses, and other components. Such operations asforming an image of an object on the sensor device 410 are alsoperformed. Focusing and other adjustments are also performed as needed.

The sensor device 410 is formed by arranging the thermal detector (thepyroelectric infrared detector 200) of the present embodiment describedabove in two dimensions, and a plurality of row lines (word lines, scanlines) and a plurality of column lines (data lines) are provided. Inaddition to the optical detector arranged in two dimensions, the sensordevice 410 may also include a row selection circuit (row driver), a readcircuit for reading data from the optical detector via the column lines,an A/D conversion unit, and other components. Image processing of anobject image can be performed by sequentially reading data from opticaldetectors arranged in two dimensions.

The image processor 420 performs image correction processing and variousother types of image processing on the basis of digital image data(pixel data) from the sensor device 410.

The processor 430 controls the electronic instrument as a whole andcontrols each block within the electronic instrument. The processor 430is realized by a CPU or the like, for example. The storage unit 440stores various types of information and functions as a work area for theprocessor 430 or the image processor 420, for example. The operatingunit 450 serves as an interface for operation of the electronicinstrument by a user, and is realized by various buttons, a GUI(graphical user interface) screen, or the like, for example. The displayunit 460 displays the image acquired by the sensor device 410, the GUIscreen, and other images, for example, and is realized by a liquidcrystal display, an organic EL display, or another type of display.

A thermal detector of one cell may thus be used as an infrared sensor orother sensor, or the thermal detector of one cell may be arranged alongorthogonal axes in two dimensions to form the sensor device 410, inwhich case a heat (light) distribution image can be provided. Thissensor device 410 can be used to form an electronic instrument forthermography, automobile navigation, a surveillance camera, or anotherapplication.

As shall be apparent, by using one cell or a plurality of cells ofthermal detectors as a sensor, it is possible to form an object analysisinstrument (measurement instrument) for analyzing (measuring) physicalinformation of an object, a security instrument for detecting fire orheat, an FA (factory automation) instrument provided in a factory or thelike, and various other electronic instruments.

FIG. 8A shows an example of the configuration of the sensor device 410shown in FIG. 7. This sensor device includes a sensor array 500, a rowselection circuit (row driver) 510, and a read circuit 520. An A/Dconversion unit 530 and a control circuit 550 may also be included. Aninfrared camera or the like used in a night vision instrument or thelike, for example, can be realized through the use of the sensor devicedescribed above.

A plurality of sensor cells is arrayed (arranged) along two axes asshown in FIG. 2, for example, in the sensor array 500. A plurality ofrow lines (word lines, scan lines) and a plurality of column lines (datalines) are also provided. The number of either the row lines or thecolumn lines may be one. In a case in which there is one row line, forexample, a plurality of sensor cells is arrayed in the direction(transverse direction) of the row line in FIG. 8A. In a case in whichthere is one column line, a plurality of sensor cells is arrayed in thedirection (longitudinal direction) of the column line.

As shown in FIG. 8B, the sensor cells of the sensor array 500 arearranged (formed) in locations corresponding to the intersectionpositions of the row lines and the column lines. For example, a sensorcell in FIG. 8B is disposed at a location corresponding to theintersection position of word line WL1 and column line DL1. Other sensorcells are arranged in the same manner. The row selection circuit 510 isconnected to one or more row lines, and selects each row line. Using aQVGA (320×240 pixels) sensor array 500 (focal plane array) such as theone shown in FIG. 8B as an example, an operation is performed forsequentially selecting (scanning) the word lines WL0, WL1, WL2, . . .WL239. In other words, signals (word selection signals) for selectingthese word lines are outputted to the sensor array 500.

The read circuit 520 is connected to one or more column lines, and readseach column line. Using the QVGA sensor array 500 as an example, anoperation is performed for reading detection signals (detectioncurrents, detection charges) from the column lines DL0, DL1, DL2, . . .DL319.

The A/D conversion unit 530 performs processing for A/D conversion ofdetection voltages (measurement voltages, attained voltages) acquired inthe read circuit 520 into digital data. The A/D conversion unit 530 thenoutputs the A/D converted digital data DOUT. Specifically, the A/Dconversion unit 530 is provided with A/D converters corresponding toeach of the plurality of column lines. Each A/D converter performs A/Dconversion processing of the detection voltage acquired by the readcircuit 520 in the corresponding column line. A configuration may beadopted in which a single A/D converter is provided so as to correspondto a plurality of column lines, and the single A/D converter is used intime division for A/D conversion of the detection voltages of aplurality of column lines.

The control circuit 550 (timing generation circuit) generates variouscontrol signals and outputs the control signals to the row selectioncircuit 510, the read circuit 520, and the A/D conversion unit 530. Acontrol signal for charging or discharging (reset), for example, isgenerated and outputted. Alternatively, a signal for controlling thetiming of each circuit is generated and outputted.

Several embodiments are described above, but it will be readily apparentto those skilled in the art that numerous modifications can be madeherein without substantively departing from the new matter and effectsof the present invention. All such modifications are thus included inthe scope of the present invention. For example, in the specification ordrawings, terms which appear at least once together with different termsthat are broader or equivalent in meaning may be replaced with thedifferent terms in any part of the specification or drawings.

Through at least one embodiment of the present invention, it is possibleto reduce curvature of the support member for supporting the thermaldetection element. This effect enables the present invention to bewidely applied to various thermal detectors (e.g., thermocouple-typeelements (thermopiles), pyroelectric elements, bolometers, and thelike). The light detected may be of any wavelength.

GENERAL INTERPRETATION OF TERMS

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Finally, terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed. For example, these terms can beconstrued as including a deviation of at least ±5% of the modified termif this deviation would not negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

1. A thermal detector comprising: a thermal detection element; a supportmember having a first side and a second side opposite from the firstside, the support member mounting and supporting the thermal detectionelement on the second side with the first side facing a cavity, thesupport member including a first layer member having a residual stressin a first direction, the first layer member being disposed on thesecond side of the support member, and a second layer member having aresidual stress in a second direction opposite to the first direction,the second layer member being laminated on the first layer member on thefirst side of the support member, a thermal conductance of the firstlayer member being less than a thermal conductance of the second layermember; and a fixing part supporting the support member.
 2. The thermaldetector according to claim 1, wherein the support member furtherincludes a third layer member laminated on the second layer member sothat the second layer member is disposed between the first layer memberand the third layer member, and the third layer member has a residualstress in the first direction.
 3. The thermal detector according toclaim 1, wherein one of the first layer member and the second layermember includes an oxide layer, and the other of the first layer memberand the second layer member includes a nitride layer.
 4. The thermaldetector according to claim 3, wherein the first layer member and thethird layer member are made of the same material.
 5. The thermaldetector according to claim 1, wherein the thermal detection elementincludes a capacitor in which an amount of polarization varies based ona temperature, the capacitor having a pyroelectric body between a firstelectrode and a second electrode.
 6. The thermal detector according toclaim 5, wherein one of the first layer member and the second layermember has reducing gas barrier properties.
 7. The thermal detectoraccording to claim 5, further comprising a reducing gas barrier layercoating at least a side surface of the capacitor, the second layermember having reducing gas barrier properties.
 8. The thermal detectoraccording to claim 6, wherein the first electrode includes anorientation control layer that controls orientation of the pyroelectricbody, and an adhesive layer that increases adhesion to the first layermember of the support member, the adhesive layer being disposed furthertoward the support member than the orientation control layer.
 9. Thethermal detector according claim 1, wherein the support member includesan etching stop layer on an outermost layer on the second side, theetching stop layer being formed on a sacrificial layer disposed in thecavity and left as the outermost layer on the second side of the supportmember after removal of the sacrificial layer.
 10. The thermal detectoraccording to claim 9, wherein the etching stop layer has reducing gasbarrier properties.
 11. A thermal detection device comprising: aplurality of the thermal detectors according to claim 1 arranged in twodimensions along two orthogonal axes.
 12. A thermal detection devicecomprising: a plurality of the thermal detectors according to claim 2arranged in two dimensions along two orthogonal axes.
 13. A thermaldetection device comprising: a plurality of the thermal detectorsaccording to claim 3 arranged in two dimensions along two orthogonalaxes.
 14. A thermal detection device comprising: a plurality of thethermal detectors according to claim 4 arranged in two dimensions alongtwo orthogonal axes.
 15. A thermal detection device comprising: aplurality of the thermal detectors according to claim 5 arranged in twodimensions along two orthogonal axes.
 16. A thermal detection devicecomprising: a plurality of the thermal detectors according to claim 6arranged in two dimensions along two orthogonal axes.
 17. A thermaldetection device comprising: a plurality of the thermal detectorsaccording to claim 7 arranged in two dimensions along two orthogonalaxes.
 18. A thermal detection device comprising: a plurality of thethermal detectors according to claim 8 arranged in two dimensions alongtwo orthogonal axes.
 19. An electronic instrument comprising: thethermal detector according to claim
 1. 20. An electronic instrumentcomprising: the thermal detection device according to claim 11.